Re: NULL pointer dereference in iio_buffer_register()

Fengguang Wu
2012-07-31T13:04:49Z

On Tue, Jul 31, 2012 at 03:06:11PM +0200, Lars-Peter Clausen wrote:
> On 07/31/2012 02:55 PM, Fengguang Wu wrote:
> >>> The panic happens while trying to dereference the NULL indio_dev->buffer:
> >>>
> >>> 266 int iio_buffer_register(struct iio_dev *indio_dev,
> >>> 267 const struct iio_chan_spec *channels,
> >>> 268 int num_channels)
> >>> 269 {
> >>> 270 struct iio_dev_attr *p;
> >>> 271 struct attribute **attr;
> >>> 272 struct iio_buffer *buffer = indio_dev->buffer;
> >>> 273 int ret, i, attrn, attrcount, attrcount_orig = 0;
> >>> 274
> >>> ==> 275 if (buffer->attrs)
> >>> 276 indio_dev->groups[indio_dev->groupcounter++] = buffer->attrs;
> >>>
> >>> iio_dummy_probe() has the code to configure that buffer, however
> >>> iio_simple_dummy_configure_buffer() is defined to do nothing on
> >>> !CONFIG_IIO_SIMPLE_DUMMY_BUFFER..
> >>>
> >>> 448 /* Configure buffered capture support. */
> >>> ==> 449 ret = iio_simple_dummy_configure_buffer(indio_dev);
> >>> 450 if (ret < 0)
> >>> 451 goto error_unregister_events;
> >>> 452
> >>> 453 /*
> >>> 454 * Register the channels with the buffer, but avoid the output
> >>> 455 * channel being registered by reducing the number of channels by 1.
> >>> 456 */
> >>> 457 ret = iio_buffer_register(indio_dev, iio_dummy_channels, 5);
> >>> 458 if (ret < 0)
> >>> 459 goto error_unconfigure_buffer;
> >>>
> >>> Any ideas to fix it?
> >>>
> >>
> >> Hi,
> >>
> >> I think the best would be to move the iio_buffer_register to
> >> iio_simple_dummy_configure_buffer.
> >
> > Lars, thanks for the quick reply! Hmm, that looks more like a code
> > refactor recommendation than fix ;) In the simplest form, can the
> > bug fixed like this?
> >
> > static inline int iio_simple_dummy_configure_buffer(struct iio_dev *indio_dev)
> > {
> > - return 0;
> > + return -1;
> > };
> >
>
> No, we want iio_simple_dummy_configure_buffer to be a noop if buffer support
> is disabled, since the driver works fine without it. Except for the issue
> you discovered. This issue only appears if CONFIG_IIO_BUFFER=y and
> CONFIG_IIO_SIMPLE_DUMMY_BUFFER=n. E.g. if both are not set the driver works
> fine without buffers.

OK.

> I can prepare a patch which moves the iio_buffer_register to
> iio_simple_dummy_configure_buffer if you want to.

That would be good, thank you very much!

Thanks,
Fengguang